Programmable RF Attenuation Project

Project goals

• Design and build a system to provide UMA test engineers a way to programmatically emulate the action of approaching / moving away from WIFI access points.

• For maximum flexibility, the system should contain multiple parameters that are configurable by the user.

• Evaluate the performance of various handsets for validation of end product.

Components required

• Faraday cage room – RF isolated room • Programmable RF attenuator (TTL inputs) • USB switch that provides TTL outputs• Cable interface to attenuator from USB switch• User windows application to drive the attenuator

Personnel

Faraday Cage Room

Programmable RF Attenuator

RF feed-through

TTLControl cable

Overall test system

Basic Stamp Attenuator Controller

• Modified Virtual COM port USB I/O device connected to any terminal software.

• Input: a valid attenuation value• Output: a binary weighted

digital output (TTL)

Modify USB Basic Stamp

• Program basic stamp• Rewire I/O to

microcontroller• Assemble IDE cable

TTL ConnAttenuator

BASIC Stamp 1

63 pinout

<model>-63 dB(cell)

BASIC Stamp 1

xx.75 pinout

<model>-63.75

dB(cell)

1 P0 1 Vss 0.25

2 P1 2 Vss 0.50

3 P2 4 P0 1

4 P3 8 P1 2

5 P4 16 P2 4

6 P5 32 P3 8

7 P4 16

8 P5 32

9 Vdd +5V Vdd +5

10 Vss COM Vss COM

P6 Pin24 BS1USB

P6 Pin24 BS1USB

P7 Pin25 BS1USB

P7 Pin25 BS1USB

USB Attenuator Micro-controller flowListen for an incoming attenuation command

from the PC on controller pin 7

Input < 64?

YES NOWe have an input, Change the attenuation

Then send it out

Keep serial pins HIGH

Read actual pin states

Delay for stablization

Convert HEX to Decimal(valid inputs from 0 to 63 in lookup table)

Controller replies to PC on pin 6“CHANGE ATTN = XX”

Read the pins

Controller replies to PC on pin 6“NO CHANGE ATTN = XX”

Look for more input Look for more input

Com Port and configurationPoint to COM port control tab

User selects port

Is Serial port Open?

YES

NO“Check USB port or

select the correct port”

Has user made listbox

selections yet?

NO

YES

Wait for user To finish making

selections

User presses START

Build file folder and date stamped

log file

Calculate attenuation rate

serialPort_dataReceived event

Invoke AddReceive event handler

Add whatever has been received to the main holder “received”

Call ReadData every ½ second thenParse incoming strings for received DB value

Do we have data?

Verification received from controller, count

the time stamp

YES

Compare incoming string to the data that

was sent out

Ignore nullstrings

NO

Desktop Attenuator control UI

Configure Hand-in / Hand-out

Hand-in / Hand-out cycle definitiondB

Time

Select Step Size

in dB

Select Time Step

(seconds)

Select StartValue (dB)

Select StopValue (dB)

Select Half Cycle

count

SelectHalf Cycle

delayHalf cycle

delayHalf Cycle

count

Hand-in / Hand-out state machine

HIHOstate1

HIHOstate0

HIHOstate1.Start()

AttnSixtyToZero()

60 seconds

HIHOstate2

HIHOstate2.Start()

1,2,3, or 5 minutes

AttnZero()

isCONNUMAimage & isCONNimage

!isCONNUMAimage & !isCONNimage ORisCALLFAILimage

HIHOtimer

HIHOstate3HIHOstate3.Start()

AttnZeroToSixty()

HIHOtimer.Start()

RIROtest&

isUMAimage

No hand-in yet ,Wait another 30

secondsRove-in occurred, 60 dB attenuation STARTING NOW

Hand-in occurred, 60 dB attenuation STARTING NOW60

seconds

HIHOstate4

AttnSixty ()

AttnSixty ()

80 seconds

HIHOstate5

!isCONNUMAimage & isCONNimage

We have handedOut to GSMPASS case

isCONNUMAimage & isCONNimage ORisCALLFAILimage

We have Hand out to GSM

FAIL case

isUMAimage&

RIROtest

Rove OutTo

GSMFAIL

!isUMAimage&

RIROtest

Rove OutTo

GSMPASS